Treatment of cellulose derivatives



April 24, 1934. DREYFUS ET AL 1,955,793

TREATMENT OF CELLULOSE DERIVATIVES Filed Aug. 19, 1930 O O O 0 3 20 1s g O O O O O C) HENRY DREYFUS WILLIAM I TAYLOR INVENTOHS Patented Apr. 24, 1934- usrrs srrss PAT iii; FFICE TREATMENT OF CELLULOSE DERIVATIVES tion of Delaware Application August 19, 1930, Serial No. 476,334 In Great Britain Gctober 3, 1929 8 Claims.

This invention relates to the production of artificial filaments, threads, ribbons or other products from solutions of cellulose acetate or other cellulose derivatives by the dry or evaporative method, i. e. by the extrusion of spinning solutions of the cellulose derivatives in volatile solvent liquids into an evaporative atmosphere.

An object of the invention is the production of filaments or products of fine or extremely fine denier or cross-section and/or of increased strength.

There is described in U. S. patent application S. No. 463,658 filed 25th June, 1930 a process of spinning filaments or products of fine or extremely fine denier or cross-section, said process consisting in extruding a spinning solution of cellulose acetate or other cellulose derivative into an evaporative atmosphere in the passage through which a substantial proportion of the volatile solvent is removed from the filaments or products, with the result that a skin-like outer layer is formed surrounding a softer or more plastic core. Thisouter layer is then softened by means of an atmosphere of solvent vapours while stretch is applied to draw out the filaments or products to the desired degree of fineness. The action of the solvent vapours on the outer skin enables or assists the stress of stretching to be withstood Without breakage, while a considerable reduction in denier can be efiected.

U. S. patent application S. No. 463,932 filed 26th June, 1930employs a similar method, but, with the object of producing filaments or products which have an increased strength, the stretch applied after the softening of the similarly formed outer layer is confined Wholly or partially to that portion of the filaments or products Which has been submitted to the softening treatment. This increase of strength is achieved Whatever denier of filament is being spun, but the invention is particularly important when employed for the production of strong filaments of fine or extremely fine denier.

It has now been found that similar advantages, either in the way of fine or extremely fine filaments or products, or of filaments or. products having an increased strength, or both, can be efiected by softening the outer skin which has been formed by the removal of volatile solvent, by the application to the filaments or products of a solvent or softener in liquid form. Thus, after the filaments have left the evaporative zone in which the skin-like outer layer is formed around an inner softer or more plastic core, they may encounter a Wick,bath, or any other means suitable for applying a liquid solvent or softener. Stretch is exerted on the softened products by a draw-roller or other suitable device, and the products are then caused or allowed to harden, as by passing them through a further evaporative atmosphere (heated or otherwise) or by washing ofi the solvent or softening liquid by means of suitable diluents having no deleterious action on the products.

If desired, the treatment with solvent or softener in the liquid form may be supplementary to a treatment with solvent vapours as described in the prior specifications referred to.

The process may be directed to the production of fine or extremely fine denier filaments, or to the production of filaments or products of increased strength, whatever their denier. For the purpose of obtaining strong filaments or other products, the applied stretch may be wholly or partially limitedto that part of the filaments or products of which the outer skin has been softened. This limitation or" the incidence of the stretch may be applied whether the filaments or products are coarse, normal, or fine, but par-- ticularly valuable results are obtained when the limitation is resorted to in spinning operations which are directed to the production of fine or extremely fine denier or cross-section, since the reduction in denier or cross-section can at the same time be accompanied by an increase of strength.

Filaments or other products produced according to the invention are particularly adapted to receive a further stretching when they have reached an elastic condition, and may be given such further stretching, whereby, as is described in U. S. patent application S. No. 378,684 filed 16th July, 1929, they are given lower denier, together with increased strength.

In carrying the invention into effect the spinning solution may, for example, be extruded downwardly into a chamber into which air or other evaporative medium is introduced, the chamber and/or the medium preierablybeing heated to stimulate a fairly rapid removal or solvent from the extruded filaments. A skin-like layer is formed on the filaments, evaporation continuing until the filaments contain an amount of solvent such as 15, 25, or 50%. The air or other medium may be intrcduced'into the chamber in the vicinity of the spinning jet, for example, by means of the slotted or perforated tubular ring or pipe or other devices described in U, S. patent application S. No. 382,907 filed 2nd August, 1929, or may flow in counter-current to the flow oi the filaments. In either case, collector devices such as are described in U. S. patent applications S. Nos. 236,448 filed 29th November, 1927 and 405,784 filed 8th November, 1929 may, if desired, be employed to constrain the medium to pass through the immediate vicinity of the jet or of the filaments proceeding from the jet. Solvent-laden medium may be withdrawn from any suitable point of the chamber, preferably in controlled amount in the manner described in U. S. Patent No. 1,541,494, and may pass to a plant for the recovery of solvent.

A liquid solvent or softener is then applied to the partially set filaments by means of a Wick or bath or other suitable means. This may be effected, for example in a chamber entirely separate from the evaporative chamber containing the spinning jet, or in a compartment formed by subdividing a larger chamber by means of a partition presenting an orifice for the passage of the filaments. The orifice may be adjustable and of such a form as to retard or prevent the passage of vapours from one chamber to the other. By suitable control of the withdrawal of solvent-laden air from the evaporative chamber, fiow between the chambers may be regulated or prevented, as desired.

Examples of liquids having a suitable solvent or softening action on the filaments are acetone, alone or mixed with alcohol or water, acetic acid, formic acid, lactic acid, acetyl acetone, dimethylethylene glycol, monomethylethylene glycol, monoethylethylene glycol, dioxane, methyl or ethyl lactate and diacetone alcohol, or mixtures thereof.

After receiving the solvent or softener, the filaments pass to a roller or other stretching device, preferably located outside the second chamber. The stretching roller may be of conical form in order to facilitate the application of stretch to the filaments, the filaments being taken round a smaller diameter when starting up and afterwards traversed on to a larger diameter when stretching is to commence or the amount of stretch increased.

Between the solvent or softener applying means and the stretching roller, further evaporation takes place from the filaments, and it is preferred to pass the filaments through an evaporative atmosphere to facilitate this removal of the solvent. For this purpose, air or other medium may be passed through the chamber containing the softening means, but it is preferred to employ a further chamber, separate from the others or formed by sub-division of a larger chamber. The stretching roller may be arranged inside or outside this further chamber. The solvent-laden medium may be withdrawn from this chamber and may be mixed with the other solvent-laden air or led separately to a recovery plant or alternatively the medium from this final drying chamber may be passed into the first chamber.

Where the solvent or softener is sufficiently volatile, the conditions in the second evaporative chamber may be such as to remove the solvent or softener as well as the solvent used in the spinning solution. In this connection, it may be noted that the applied liquid may consist of or contain the same solvent as that employed in the spinning solution. If, however, the solvent or softener is not wholly removed by these means, the filaments may be subjected to washing with suitable diluents for the solvent or softener, preferably after passing the stretching roller.

The denier or cross-section of the filaments or other products depends, of course, on the concentration of the spinning solution, on the size of the nozzles and on the extent of the applied stretch. In order to get extremely fine deniers which are at the same time strong, the filaments are extruded in a manner which in normal dry-spinning processes would give a low denier, and the application of the several steps of the present invention results in the reduction of the denier still further, to an extent hitherto unobtainable.

In order to produce filaments 01' products of still further increased strength, means may be provided to confine the stretch wholly or partly to the softened part.

Thus, after the passage of the filaments through the first evaporative chamber, and before or during the application of the solvent or softener, the filaments or other products may encounter means such as a roller, guide, or tension device which offers a resistance to their passage, the amount of the resistance determining whether the stretch is in part allowed to extend to the unsoftened filaments or wholly confined to the softened portion. Thus, the filaments may be caused to pass through a gate-tension device, which is preferably adjustable to enable its resistance to be regulated. A form of tension device particularly suitable for the purpose comprises twogates of polished steel bars, adjust ment being provided to cause the bars of the two gates to intermesh. The gates may be arranged to open apart to allow the filaments to pass down the chamber on starting up, and, when stretch is to be imparted are adjusted to give the requiste tension by the intermeshing of the bars. Other arrangements of two or more bars may be employed to offer the required resistance by their engagement with the filaments.

Alternatively, a roller may be arranged to receive the filaments, this roller being allowed or caused to rotate at a peripheral speed either equal to or greater than the speed of extrusion, according to whether the stretch is to be wholly or partly restricted to the softened part of the filaments.

The means for confining the stretch may be combined with the means for applying the solvent or softener. Thus, when one or more wicks are used to apply the solvent or softener, the

passage of the filaments over the wick or wicks may be caused to restrict the stretch. Resistance may be imparted gradually, and, if desired, simultaneously with the traversing of the filaments on to the larger diameter of the conical stretching roller.

By applying restricted stretch as described above, stronger filaments are produced, and by applying this stretch together with conditions which would normally give low denier filaments, fine or extremely fine filaments can be produced which at the same time exhibit this increased strength.

In order to facilitate the stretching of the softened filaments and produce filaments of increased strength, plasticizers or high boiling solvents may be added to the spinning solutions. Thus, for example, with spinning solutions containing cellulose acetate, higher-boiling solvents,

its

such as cyclobutanone, acetyl-acetone, diacetone alcohol, dimethyl ethylene glycol, monomethylethylene glycol, monoethylethylene glycol, or plasticizers such as methyl or ethyl Xylene sulphonamides, or mixtures thereof may be added to the solutions. Such plasticizers can afterwards remain in the filaments, or, if necessary,

they may be removed, e. g., by extraction with a solvent for the plasticizer, which-at the same time is not a solvent for the cellulose derivative employed. r

As previously stated, filaments produced according to the invention are specially suitable for receiving further stretch after they have become elastic, and, therefore, such further stretch may be applied, continuously with their production. The filaments may be stretched in the presence of a suitable agent or agents in liquid or vapour form to facilitate thestretohing, the agent or agents being applied either before or during the stretching operation, or even contained in the spinning solution, as described in U. S. patent application S. No. 378,684. Thus, for example, the further stretching may be imparted to the filaments after they have left the stretching roller employed for extending the softened filaments, a residuum of solvent or softener not removed by evaporation or otherwise assisting the further stretching operation. The high-boiling solvents or plasticizers, where such are used in the spinning solution, may also serve as assisting agents. Alternatively, the assisting agent or agents may be applied to the filaments after they have left the chambers of the spinning apparatus, and preferably after they have left the stretching roller.

The filaments or threads of associated filaments may be collected by means of suitable winding or twisting and winding devices, e. g., the cap-spinning devices described in U. S. Patent No. 1,731,317, operations such as lubricating, moistening, or sizing being performed on the filaments or threads continuously with their production.

Examples of organic derivatives of cellulose from solutions of which the filaments or threads may be produced, in addition to cellulose acetate, are cellulose formate, propionate, and butyrate, methyl, ethyl, and benzyl cellulose, and the corresponding condensation products of cellulose and glycols or other polyhydric alcohol.

The accompanying drawing shows diagram-v matically one means of oarrying'the invention into effect, in which the first evaporative chamber, a chamber for applying the softening or solvent liquid and the final setting chamber, all form part of a single cell. It will be appreciated however that the invention is by no means limited thereto.

A 20-28% solution of cellulose acetate in acetone, which may, if desired, contain 520% of diacetone alcohol or methyl or ethyl lactate (calculated on the cellulose acetate), is extruded through a spinning nozzle 2 into a cell 3, the fila-f ments being carried round a guide 4, out of the 1 cell and round a conical feed roller 5. The cell 3 is sub-divided into compartments by means of partitions provided with suitable openings for the passage of the filaments. The upper compartment '7, which should be of such a length, for example 4-8 inches from spinning nozzle to partition, as to leave a substantial proportion of solvent still in the filaments, is provided with suitable heating pipes 8 to accelerate the formation of an outer skin-like layer on the filaments. After passing through the compartment '7 the filaments enter by means of the opening 9 the compartment 10 in which they contact with wicks or other means 11 supplied with a softening or solvent liquid from tanks 12 through flexible pipes 13, valves 14 serving to control the supply and tubes 15 adjustably mounted in trunnions 16 in the walls of the cell and carrying wedge-shaped members 1'7, perforated at the extreme ends. The'filaments are softened during their passage through the compartment 10, the amount of softening being determined chiefly by the nature and concentration of the liquid applied. Various liquids may be used for example aqueous acetone, 50% alcoholic acetone, or 50-60% dioxane, diacetone alcohol'or methyl or ethyl lactate. The softened filaments pass by an opening 18 into the final drying chamber 19 furnished with heating pipes 20. Air or other suitable medium is admitted at 21 into the compartment 19 and passes by way of a pipe 22 directly from the compartment 19 to the upper compartment 7 and finally through a suitable control 23 and main collector pipe 24 to the solvent recovery plant.

The openings 9 and 18 are preferably adjustable in size, for example of the iris diaphragm type, so that upon starting up the filaments may be passed easily from one compartment to the next. Initially they are opened wide and the tubes 15 are drawn back through the trunnions 16 to their fullest extent. The filaments are carried in the ordinary manner to the guide 4, out of the cell, and round the small diameter of the conical roller 5. The upper tube 15 (to the left of the figure) is then pushed forward gently so as to contact with the filaments and to take up approximately the position shown in the figure. The lower tube 15 (to the right of the figure) is then brought into contact with the filaments and adjusted in position so as to divert them through a considerable angle. The angles through which the filaments are so diverted will determine whether the whole 01' what proportion of the stretch imparted by the roller 5 is confined to the softened portion of the filaments. As previously indicated, to obtain very strong filaments, all or most of the stretch should be so confined. The filaments are then traversed to the large diameter of the conical roller 5 so as to insert the required stretch, the peripheral speed being then, for example, 2 to 5 times or more that of the speed of extrusion. Finally the openings 9 and 18 are adjusted so as to allow only a small proportion of the air or other medium from compartment 19 to pass into compartment 10 and finally into compartment 7. The filaments after passage round the roller '5 may be passed to a cap spinning device 6 or other winding device or to a further feed roller by means of which additional stretch may be imparted, if desired.

The effect of the softening treatment in the compartment 10 is enhanced by the presence in the spinning solution of a relatively high boiling solvent or softening agent, though it is to be understood that this may be omitted if desired. Instead of passing the filaments through a final evaporating chamber 19, they may be passed into a skin-like outer layer, applying a liquid solvent or softening agent and stretching and completing the setting of the products.

2. Process according to claim 1, wherein the setting of the products is completed by the dry or evaporative method.

6. Process according to claim 1, wherein the spinning solution contains an organic derivative of cellulose.

7. Process according to claim 1, wherein the spinning solution contains an organic derivative of cellulose and a relatively high boiling solvent material.

8. Process according to claim 1, wherein the spinning solution contains cellulose acetate and a relatively high boiling solvent material.

HENRY DREYFUS. WILLIAM IVAN TAYLOR. 

